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No. 609,990. Patented Aug. 30, I898.

B. G. LANNE. NEANS FOR CONTROLLING NON-SYNOHRONOUS ALTERNATING CURRENTIOTORS.

' (Appliention filed In. 11, 1896.)

(No Nodal.)

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. UNITED STATES PATENT OFFICE.

BENJAMIN G. LAMME, OF PITTSBURG, PENNSYLVANIA, ASSIGNOR TO THE\VESTINGHOUSE ELECTRIC AND MANUFACTURING COMPANY, OF SAME PLACE.

MEANS FOR CONTROLLING NON-SYNCHRONOUS ALTERNATlNG-CURRENT MOTORS.

SPECIFICATION forming part of Letters Patent No. 609,990, dated August30, 1898.

Application filed March 11, 1896. Serial No. 582,765. (No model.)

To all whom it may concern: square of the electromotive force applied.

Be it known that I, BENJAMIN G. LAMME, a The form of the curverepresenting the torque citizen of the United States, residing inPittsfor the lower primary electromotive force is burg, in the county ofAllegheny and St-ateof similar to that for the higher; but the drop 5Pennsylvania, have invented a new and usein speed for a given torque ismuch greater.

ful Improvement in Means for Controlling By varying the electromotiveforce applied to Non-Synchronous Alternating- Current Mosuch a motor thespeed may therefore be vators, (Case No. 686,) of which the followingisried over a wide range. This variation of a specification. electromotiveforce may be obtained by any [0 Myinvention relates toalternating-current suitable 'means; but a convenient means forelectricmotors of that class known as inthis purpose consists oftransformers production-motors, in which the current issupvided withvariable ratios of transformation. plied to the primary member and thesecond- This variation in the electromotive force supary member hasclosed-circuit windings in plied by the transformers maybe secured by I5 which current is induced by that supplied to varying the effectivelengths of either their the primary member. primaries or theirsecondaries or by varying The object of my invention is to provide a therelative position of the two. A variable means whereby a variable speedand a large resistance in the primary circuit is not satisstartingtorque may be secured with inducfactory for the purpose of securingvariations 2o tion-motors in which the magnetic leakage is inelectromotive force, for the reason that as small and the secondarymembers have highthe electromotive force applied to the motor resistancewindings. is reduced the current for a given torque is My invention isdesigned more particularly increased. Consequently the watts suppliedfor motors operated by multiphase currents; to the motor areapproximately constant and 25 but it may be employed in connection withthe resistance in the circuit would involve a single-phase motors undercertain conditions. very considerable loss. As has already been It hasbeen found in practice that an alterstated, a motor suitable for givingsatisfacnating-current motor of the non-synchronous tory results inconnection with the method of type will tend to run at an approximatelyconregulation above outlined is one in which the 0 stant speed and thatin order to secure an magnetic leakage between the primary and increaseof torque with a drop in speed bethe secondary is very small and inwhich the low such value the secondary member of the resistance of thesecondary circuit is commotor must have considerable resistance andparatively very large.

a small amount of self-induction. If the re- Figure 1 is a diagramillustrative of my in- 3 5 sistance in the secondaryis small and theselfvention in which hand-operated means for induction large, the torquewill be at a maxivarying the voltage supplied to the primary mum whenthe motor is running at a commember of the motor are provided and inparatively high speed and will decrease with which the motor has ahigh-resistance seethe decrease in speed from that point. If, ondary.Fig. 2 is a diagram indicating the 40 however, the motor is soconstructed that the torque in terms of speed in motors having lowmagnetic leakage between the primary and magnetic leakageandcomparatively highsecsecondary is very low and the resistance inondary resistance, and Fig. 8 is a diagram inthe secondary is high, themaximum torque dicating the torque in terms of speed in a mo of themotor may be secured at zero speed. tor of usual construction in whichthere is a 45 If the electromotive force applied to the prigreatermagnetic leakage between the primary of a motor of the character lastabove mary and secondary and in which the secdescribed be decreased, themaximum torque ondary has a comparatively low resistance. will bedecreased in a greater degree, the law Referring more particularly tothe drawbeing that the maximum torque varies as the ings, 1 is atwo-phase induction motor the primary member of which is supplied withenergy from the secondaries of two transformers 2 and 3, the primariesof such transformers being supplied from a two-phase generator 4. Eachof the transformers 2 and 3 is shown as provided with a dividedsecondary having branching conductors which terminate in a series ofcontact-points 5. A contact bar or'strip 6 is located parallel to eachseries of contact-points 5, a movable contact device 7 being so locatedas to make electrical connection between any contact-point of the seriesand the adjacent strip 6. It will be readily understood that by this orany equivalent meansI am enabled to include a greater or less portion ofthe length of the secondary coil in circuit,whereby the electromotiveforce applied to the primary winding of the motor 1 may be varied inorder to secure variable speed with a maximum starting torque.

8 are ordinary current-indicating instruments connected with the circuitsupplying the primaries of the transformers 2 and 3.

In each of Figs. 2 and 3 speed is indicated on the line 9 and torque onthe line 10. It will be observed from the curved full line 12 of Fig. 2,which indicates the torquejn terms of speed, that the maximum torque issecured at zero speed, which is a desirable condition in motors employedfor moving loads frequent starting and stopping of which are necessary.The broken line 12 indicates the torque in terms of speed at a reducedvoltage. This diagram indicates the conditions in motors in which themagnetic leakage is small and the secondary resistance comparativelyhigh. As indicated in Fig. 3, the torque in terms of speed representedby the line 13 shows that the torque at zero speed is only a fraction ofthat which is exerted when the motor is running at a comparatively highspeed near synchronism. This reduction in torque at low speed is not ofmaterial consequence in motors which are employed for work requiring anapproximately uniform speed; but it is obviously not suitable for usewhere frequent stopping and starting are necto the primary memberwhereby the speed of the motor is varied.

2. A variable-speed, non-synchronous motor having a comparatively largesecondary resistance and a small degree of magnetic leakage between itsprimary and secondary members, in combination with means for varyin gthe electromotive force applied to its primary member, whereby the speedof the motor is varied.

3. The combination with an induction-motor having small magnetic leakageand a highresistance secondary circuit, of means for varying the speedof said motor consisting of a transformer or transformers for supplyingcurrent to the primary Winding of the motor and means for varying therelation between the primary and secondary coils, and thereby varyingthe electromotive force supplied by the secondary.

4. The combination with a polyphase in duction-motor having ahigh-resistance secondary winding directly short-circuited on itself, oftransformers for supplying current to the primary member thereof, andmeans for varying the active lengths of the secondaries of suchtransformers whereby the electromotive force applied to the primary ofthe motor is varied, in order to vary the speed of the motor.

In testimony whereof I have hereunto subscribed my name this 7th day ofMarch, A. D.

BENJ. G. LAMME.

Witnesses:

WESLEY G. CARR, HUBERT O. TENER.

